The OMCD is known to possess an active apical H+-K+ATPase and a basolateral Na+-K+ pump. Homeostatic adaptive increases in the activities of both transporters in the OMCD have been reported in potassium-deficient and potassium-loaded animals, respectively (Wingo, AJP 253:F1136, 1987; Doucet & Katz, AJP 238:F380, 1980). These adaptive mehanisms imply that the OMCD experiences significant K+ fluxes and raises the physiological need for K+ exit pathways. Previous whole-cell patch experiments in rabbit OMCD cells in primary culture reported a small K+ conductance (Pappas & Koeppen, AJP 263:F1004, 1992). Moreover the ROMK1 isoform of the KATP channel has been demonstrated in rat OMCD segments by in situ hybridization (Lee & Hebert, AJP 268:F1124, 1995). Nevertheless, results of single channel studies have not been reported. The aim of this study was to identify K+-selective channels in the OMCD. Using the patch clamp technique, we have demonstrated K+-selective (K+:Na+ = 20:1) channels in the apical membrane of OMCD, cells, a cell line previously characterized by Hays & Alpem (JASN 3:779, 1992). In symmetrical (140 mM KCI) solutions, the single channel conductance was 67.0 ±4.3 pS for inward currents and 34.3 ±2.3 pS for outward currents. In the excised (inside-out) state, the channel was sensitive to intracellular barium (2 mM) but insensitive to voltage and micromolar [Ca2+]. The NP0 was reduced from 0.60 ±0.06 to 0.05 ±0.03 with the addition of ATP (2 mM) and returned to 0.53 ±0.04 after removing ATP (n=3). These KATP channels may be the equivalent of the ROMK1 isoform in rat OMCD segments, and could serve as apical K+-exit pathways in the OMCD, to accomplish K+ secretion and/or K+ recycling.
|Original language||English (US)|
|Journal||Journal of Investigative Medicine|
|State||Published - 1996|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)